Series of measurements were carried out with volunteers with and without relevant soccer heading experience, and the impact velocity of the striking head was measured. A soccer ball was used as a surrogate of the stationary victim’s head. Two scenarios were considered: one corresponding to the typical headbutt situation, i.e. short movement of the assailant’s head without backswing, and one representing the worst case, i.e. the most severe head impact without time or space constraints for the assailant.

They found that a “typical headbutt” probably won’t kill the recipient, although in some case, lethal injuries do occur. And as for the victim’s face, well, the bony parts can easily get injured. One bonus finding: “the (soccer) heading experience does not influence the velocity of the headbutt.”

There are several medical case studies involving head butts. Like this one, actually called “A troublesome head-butt” published in The Lancet. The authors write:

A 32-year-old man suffered a deep laceration to the forehead caused by contact with human teeth after a head-butting incident. He presented with a discharging wound 1 week later to his family doctor who prescribed flucloxacillin 250 mg four times a day. 10 days later, when his symptoms had worsened, the dose was increased to 500 mg four times a day. A wound swab grew Streptococcus milleri. He presented to the referring hospital 4 days later with fever and headaches.

The problem wasn’t so much the head-to-head contact, but the “contact with human teeth”:

Human bites can lead to serious infection and complications. Bacteria recovered from human bites include a mixture of aerobic and anaerobic bacteria. Streptococci (including S milleri) cause up to 70% of brain abscesses and frequently occur in mixed infections. These bacteria are normal oral commensals. Antibiotic therapy is generally recommended for all patients with human bite wounds, with coamoxiclav (amoxicillin and clavulanic acid) being the antibiotic of choice. Facial bites can have serious complications and this case highlights the need for early, aggressive, and appropriate management.

So Zidane and his head butt victim were probably fine. But you shouldn’t go around head butting people willy-nilly. If you really must head butt, here is the definitive eHow guide:

Strike your opponent quickly. Snap your neck forward and make contact with the bridge of their nose, eyebrow area, or cheek bones. These are the most vulnerable parts of your opponent’s face. Be sure that your strike is quick and specific; if you hedge at all, you will do more damage to yourself than your opponent.

About Rose Eveleth

Rose Eveleth is a writer for Smart News and a producer/designer/ science writer/ animator based in Brooklyn. Her work has appeared in the New York Times, Scientific American, Story Collider, TED-Ed and OnEarth.